/*
    * Licensed to the Apache Software Foundation (ASF) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * The ASF licenses this file to You under the Apache License, Version 2.0
    * (the "License"); you may not use this file except in compliance with
    * the License.  You may obtain a copy of the License at
    *
    *      https://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package org.apache.commons.codec.binary;
  
  import java.math.BigInteger;
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.Objects;
  import java.util.function.Supplier;
  
  import org.apache.commons.codec.BinaryDecoder;
  import org.apache.commons.codec.BinaryEncoder;
  import org.apache.commons.codec.CodecPolicy;
  import org.apache.commons.codec.DecoderException;
  import org.apache.commons.codec.EncoderException;
  
  /**
   * Abstract superclass for Base-N encoders and decoders.
   *
   * <p>
   * This class is thread-safe.
   * </p>
   * <p>
   * You can set the decoding behavior when the input bytes contain leftover trailing bits that cannot be created by a valid encoding. These can be bits that are
   * unused from the final character or entire characters. The default mode is lenient decoding.
   * </p>
   * <ul>
   * <li>Lenient: Any trailing bits are composed into 8-bit bytes where possible. The remainder are discarded.</li>
   * <li>Strict: The decoding will raise an {@link IllegalArgumentException} if trailing bits are not part of a valid encoding. Any unused bits from the final
   * character must be zero. Impossible counts of entire final characters are not allowed.</li>
   * </ul>
   * <p>
   * When strict decoding is enabled it is expected that the decoded bytes will be re-encoded to a byte array that matches the original, i.e. no changes occur on
   * the final character. This requires that the input bytes use the same padding and alphabet as the encoder.
   * </p>
   */
  public abstract class BaseNCodec implements BinaryEncoder, BinaryDecoder {
  
      /**
       * Builds {@link Base64} instances.
       *
       * @param <T> The codec type to build.
       * @param <B> The codec builder subtype.
       * @since 1.17.0
       */
      public abstract static class AbstractBuilder<T, B extends AbstractBuilder<T, B>> implements Supplier<T> {
  
          /**
           * Clones the given array or returns a default array if the array is null.
           *
           * @param array        The array to test and clone if not null.
           * @param defaultArray The default array to return if the array is null.
           * @return A clone of the array or the default array if the array is null.
           */
          static byte[] clone(final byte[] array, final byte[] defaultArray) {
              return array != null ? array.clone() : defaultArray;
          }
  
          private int unencodedBlockSize;
          private int encodedBlockSize;
          private CodecPolicy decodingPolicy = DECODING_POLICY_DEFAULT;
          private int lineLength;
          private byte[] lineSeparator = CHUNK_SEPARATOR;
          private final byte[] defaultEncodeTable;
          private byte[] encodeTable;
          private byte[] decodeTable;
  
          /** Padding byte. */
          private byte padding = PAD_DEFAULT;
  
          AbstractBuilder(final byte[] defaultEncodeTable) {
              this.defaultEncodeTable = defaultEncodeTable;
              this.encodeTable = defaultEncodeTable;
          }
  
          /**
           * Returns this instance typed as the subclass type {@code B}.
           * <p>
           * This is the same as the expression:
           * </p>
           *
           * <pre>
           * (B) this
           * </pre>
          *
          * @return {@code this} instance typed as the subclass type {@code B}.
          */
         @SuppressWarnings("unchecked")
         B asThis() {
             return (B) this;
         }
 
         byte[] getDecodeTable() {
             return decodeTable;
         }
 
         CodecPolicy getDecodingPolicy() {
             return decodingPolicy;
         }
 
         int getEncodedBlockSize() {
             return encodedBlockSize;
         }
 
         byte[] getEncodeTable() {
             return encodeTable;
         }
 
         int getLineLength() {
             return lineLength;
         }
 
         byte[] getLineSeparator() {
             return lineSeparator;
         }
 
         byte getPadding() {
             return padding;
         }
 
         int getUnencodedBlockSize() {
             return unencodedBlockSize;
         }
 
         /**
          * Sets the decode table.
          *
          * @param decodeTable The decode table.
          * @return {@code this} instance.
          * @since 1.20.0
          */
         public B setDecodeTable(final byte[] decodeTable) {
             this.decodeTable = clone(decodeTable, null);
             return asThis();
         }
 
         /**
          * Sets the decode table.
          *
          * @param decodeTable The decode table, null resets to the default.
          * @return {@code this} instance.
          */
         B setDecodeTableRaw(final byte[] decodeTable) {
             this.decodeTable = decodeTable;
             return asThis();
         }
 
         /**
          * Sets the decoding policy.
          *
          * @param decodingPolicy The decoding policy, null resets to the default.
          * @return {@code this} instance.
          */
         public B setDecodingPolicy(final CodecPolicy decodingPolicy) {
             this.decodingPolicy = decodingPolicy != null ? decodingPolicy : DECODING_POLICY_DEFAULT;
             return asThis();
         }
 
         /**
          * Sets the encoded block size, subclasses normally set this on construction.
          *
          * @param encodedBlockSize The encoded block size, subclasses normally set this on construction.
          * @return {@code this} instance.
          */
         B setEncodedBlockSize(final int encodedBlockSize) {
             this.encodedBlockSize = gte0(encodedBlockSize);
             return asThis();
         }
 
         /**
          * Sets the encode table.
          *
          * @param encodeTable The encode table, null resets to the default.
          * @return {@code this} instance.
          */
         public B setEncodeTable(final byte... encodeTable) {
             this.encodeTable = clone(encodeTable, defaultEncodeTable);
             return asThis();
         }
 
         /**
          * Sets the encode table.
          *
          * @param encodeTable The encode table, null resets to the default.
          * @return {@code this} instance.
          */
         B setEncodeTableRaw(final byte... encodeTable) {
             this.encodeTable = encodeTable != null ? encodeTable : defaultEncodeTable;
             return asThis();
         }
 
         /**
          * Sets the line length.
          *
          * @param lineLength The line length, less than 0 resets to the default.
          * @return {@code this} instance.
          */
         public B setLineLength(final int lineLength) {
             this.lineLength = Math.max(0, lineLength);
             return asThis();
         }
 
         /**
          * Sets the line separator.
          *
          * @param lineSeparator The line separator, null resets to the default.
          * @return {@code this} instance.
          */
         public B setLineSeparator(final byte... lineSeparator) {
             this.lineSeparator = clone(lineSeparator , CHUNK_SEPARATOR);
             return asThis();
         }
 
         /**
          * Sets the padding byte.
          *
          * @param padding The padding byte.
          * @return {@code this} instance.
          */
         public B setPadding(final byte padding) {
             this.padding = padding;
             return asThis();
         }
 
         /**
          * Sets the unencoded block size, subclasses normally set this on construction.
          *
          * @param unencodedBlockSize The unencoded block size, subclasses normally set this on construction.
          * @return {@code this} instance.
          */
         B setUnencodedBlockSize(final int unencodedBlockSize) {
             this.unencodedBlockSize = gte0(unencodedBlockSize);
             return asThis();
         }
     }
 
     /**
      * Holds thread context so classes can be thread-safe.
      *
      * This class is not itself thread-safe; each thread must allocate its own copy.
      */
     static class Context {
 
         /**
          * Placeholder for the bytes we're dealing with for our based logic. Bitwise operations store and extract the encoding or decoding from this variable.
          */
         int ibitWorkArea;
 
         /**
          * Placeholder for the bytes we're dealing with for our based logic. Bitwise operations store and extract the encoding or decoding from this variable.
          */
         long lbitWorkArea;
 
         /**
          * Buffer for streaming.
          */
         byte[] buffer;
 
         /**
          * Position where next character should be written in the buffer.
          */
         int pos;
 
         /**
          * Position where next character should be read from the buffer.
          */
         int readPos;
 
         /**
          * Boolean flag to indicate the EOF has been reached. Once EOF has been reached, this object becomes useless, and must be thrown away.
          */
         boolean eof;
 
         /**
          * Variable tracks how many characters have been written to the current line. Only used when encoding. We use it to make sure each encoded line never
          * goes beyond lineLength (if lineLength &gt; 0).
          */
         int currentLinePos;
 
         /**
          * Writes to the buffer only occur after every 3/5 reads when encoding, and every 4/8 reads when decoding. This variable helps track that.
          */
         int modulus;
 
         /**
          * Returns a String useful for debugging (especially within a debugger.)
          *
          * @return A String useful for debugging.
          */
         @Override
         public String toString() {
             return String.format("%s[buffer=%s, currentLinePos=%s, eof=%s, ibitWorkArea=%s, lbitWorkArea=%s, " + "modulus=%s, pos=%s, readPos=%s]",
                     this.getClass().getSimpleName(), Arrays.toString(buffer), currentLinePos, eof, ibitWorkArea, lbitWorkArea, modulus, pos, readPos);
         }
     }
 
     /**
      * End-of-file marker.
      *
      * @since 1.7
      */
     static final int EOF = -1;
 
     /**
      * MIME chunk size per RFC 2045 section 6.8.
      *
      * <p>
      * The {@value} character limit does not count the trailing CRLF, but counts all other characters, including any equal signs.
      * </p>
      *
      * @see <a href="https://www.ietf.org/rfc/rfc2045">RFC 2045 section 6.8</a>
      */
     public static final int MIME_CHUNK_SIZE = 76;
 
     /**
      * PEM chunk size per RFC 1421 section 4.3.2.4.
      *
      * <p>
      * The {@value} character limit does not count the trailing CRLF, but counts all other characters, including any equal signs.
      * </p>
      *
      * @see <a href="https://tools.ietf.org/html/rfc1421">RFC 1421 section 4.3.2.4</a>
      */
     public static final int PEM_CHUNK_SIZE = 64;
     private static final int DEFAULT_BUFFER_RESIZE_FACTOR = 2;
 
     /**
      * Defines the default buffer size - currently {@value} - must be large enough for at least one encoded block+separator
      */
     private static final int DEFAULT_BUFFER_SIZE = 8192;
 
     /**
      * The maximum size buffer to allocate.
      *
      * <p>
      * This is set to the same size used in the JDK {@link ArrayList}:
      * </p>
      * <blockquote> Some VMs reserve some header words in an array. Attempts to allocate larger arrays may result in OutOfMemoryError: Requested array size
      * exceeds VM limit. </blockquote>
      */
     private static final int MAX_BUFFER_SIZE = Integer.MAX_VALUE - 8;
 
     /** Mask used to extract 8 bits, used in decoding bytes */
     protected static final int MASK_8BITS = 0xff;
 
     /**
      * Byte used to pad output.
      */
     protected static final byte PAD_DEFAULT = '='; // Allow static access to default
 
     /**
      * The default decoding policy.
      *
      * @since 1.15
      */
     protected static final CodecPolicy DECODING_POLICY_DEFAULT = CodecPolicy.LENIENT;
 
     /**
      * Chunk separator per RFC 2045 section 2.1.
      *
      * @see <a href="https://www.ietf.org/rfc/rfc2045">RFC 2045 section 2.1</a>
      */
     static final byte[] CHUNK_SEPARATOR = { '\r', '\n' };
 
     /**
      * The empty byte array.
      */
     static final byte[] EMPTY_BYTE_ARRAY = {};
 
     /**
      * Create a positive capacity at least as large the minimum required capacity. If the minimum capacity is negative then this throws an OutOfMemoryError as
      * no array can be allocated.
      *
      * @param minCapacity The minimum capacity.
      * @return The capacity.
      * @throws OutOfMemoryError if the {@code minCapacity} is negative.
      */
     private static int createPositiveCapacity(final int minCapacity) {
         if (minCapacity < 0) {
             // overflow
             throw new OutOfMemoryError("Unable to allocate array size: " + (minCapacity & 0xffffffffL));
         }
         // This is called when we require buffer expansion to a very big array.
         // Use the conservative maximum buffer size if possible, otherwise the biggest required.
         //
         // Note: In this situation JDK 1.8 java.util.ArrayList returns Integer.MAX_VALUE.
         // This excludes some VMs that can exceed MAX_BUFFER_SIZE but not allocate a full
         // Integer.MAX_VALUE length array.
         // The result is that we may have to allocate an array of this size more than once if
         // the capacity must be expanded again.
         return Math.max(minCapacity, MAX_BUFFER_SIZE);
     }
 
     /**
      * Gets a copy of the chunk separator per RFC 2045 section 2.1.
      *
      * @return The chunk separator.
      * @see <a href="https://www.ietf.org/rfc/rfc2045">RFC 2045 section 2.1</a>
      * @since 1.15
      */
     public static byte[] getChunkSeparator() {
         return CHUNK_SEPARATOR.clone();
     }
 
     private static int gte0(final int value) {
         if (value < 0) {
             throw new IllegalArgumentException("value must be greater than or equal to 0.");
         }
         return value;
     }
 
     /**
      * Checks if a byte value is whitespace or not.
      *
      * @param byteToCheck The byte to check.
      * @return true if byte is whitespace, false otherwise.
      * @see Character#isWhitespace(int)
      * @deprecated Use {@link Character#isWhitespace(int)}.
      */
     @Deprecated
     protected static boolean isWhiteSpace(final byte byteToCheck) {
         return Character.isWhitespace(byteToCheck);
     }
 
     /**
      * Increases our buffer by the {@link #DEFAULT_BUFFER_RESIZE_FACTOR}.
      *
      * @param context     The context to be used.
      * @param minCapacity The minimum required capacity.
      * @return The resized byte[] buffer.
      * @throws OutOfMemoryError if the {@code minCapacity} is negative.
      */
     private static byte[] resizeBuffer(final Context context, final int minCapacity) {
         // Overflow-conscious code treats the min and new capacity as unsigned.
         final int oldCapacity = context.buffer.length;
         int newCapacity = oldCapacity * DEFAULT_BUFFER_RESIZE_FACTOR;
         if (Integer.compareUnsigned(newCapacity, minCapacity) < 0) {
             newCapacity = minCapacity;
         }
         if (Integer.compareUnsigned(newCapacity, MAX_BUFFER_SIZE) > 0) {
             newCapacity = createPositiveCapacity(minCapacity);
         }
         final byte[] b = Arrays.copyOf(context.buffer, newCapacity);
         context.buffer = b;
         return b;
     }
 
     /**
      * Returns a byte-array representation of a {@code BigInteger} without sign bit.
      * <p>
      * The value {@link BigInteger#ZERO} maps to an empty array.
      * </p>
      *
      * @param bigInt {@code BigInteger} to be converted.
      * @return A byte array representation of the BigInteger parameter.
      */
     static byte[] toUnsignedBytes(final BigInteger value) {
         byte[] unsigned = value.equals(BigInteger.ZERO) ? EMPTY_BYTE_ARRAY : value.toByteArray();
         if (unsigned.length > 0 && unsigned[0] == 0) {
             final byte[] tmp = new byte[unsigned.length - 1];
             System.arraycopy(unsigned, 1, tmp, 0, tmp.length);
             unsigned = tmp;
         }
         return unsigned;
     }
 
     /**
      * Deprecated: Will be removed in 2.0.
      * <p>
      * Instance variable just in case it needs to vary later
      * </p>
      *
      * @deprecated Use {@link #pad}. Will be removed in 2.0.
      */
     @Deprecated
     protected final byte PAD = PAD_DEFAULT;
 
     /** Pad byte. Instance variable just in case it needs to vary later. */
     protected final byte pad;
 
     /** Number of bytes in each full block of unencoded data, for example 4 for Base64 and 5 for Base32 */
     private final int unencodedBlockSize;
 
     /** Number of bytes in each full block of encoded data, for example 3 for Base64 and 8 for Base32 */
     private final int encodedBlockSize;
 
     /**
      * Chunksize for encoding. Not used when decoding. A value of zero or less implies no chunking of the encoded data. Rounded down to the nearest multiple of
      * encodedBlockSize.
      */
     protected final int lineLength;
 
     /**
      * Size of chunk separator. Not used unless {@link #lineLength} &gt; 0.
      */
     private final int chunkSeparatorLength;
 
     /**
      * Defines the decoding behavior when the input bytes contain leftover trailing bits that cannot be created by a valid encoding. These can be bits that are
      * unused from the final character or entire characters. The default mode is lenient decoding. Set this to {@code true} to enable strict decoding.
      * <ul>
      * <li>Lenient: Any trailing bits are composed into 8-bit bytes where possible. The remainder are discarded.</li>
      * <li>Strict: The decoding will raise an {@link IllegalArgumentException} if trailing bits are not part of a valid encoding. Any unused bits from the final
      * character must be zero. Impossible counts of entire final characters are not allowed.</li>
      * </ul>
      * <p>
      * When strict decoding is enabled it is expected that the decoded bytes will be re-encoded to a byte array that matches the original, i.e. no changes occur
      * on the final character. This requires that the input bytes use the same padding and alphabet as the encoder.
      * </p>
      */
     private final CodecPolicy decodingPolicy;
 
     /**
      * Decode table to use.
      */
     final byte[] decodeTable;
 
     /**
      * Encode table.
      */
     final byte[] encodeTable;
 
     /**
      * Constructs a new instance for a subclass.
      *
      * @param builder How to build this portion of the instance.
      * @since 1.20.0
      */
     protected BaseNCodec(final AbstractBuilder<?, ?> builder) {
         this.unencodedBlockSize = gte0(builder.unencodedBlockSize);
         this.encodedBlockSize = gte0(builder.encodedBlockSize);
         final boolean useChunking = builder.lineLength > 0 && builder.lineSeparator.length > 0;
         this.lineLength = useChunking ? builder.lineLength / builder.encodedBlockSize * builder.encodedBlockSize : 0;
         this.chunkSeparatorLength = builder.lineSeparator.length;
         this.pad = builder.padding;
         this.decodingPolicy = Objects.requireNonNull(builder.decodingPolicy, "codecPolicy");
         this.encodeTable = Objects.requireNonNull(builder.getEncodeTable(), "builder.getEncodeTable()");
         this.decodeTable = builder.getDecodeTable();
     }
 
     /**
      * Constructs a new instance.
      * <p>
      * Note {@code lineLength} is rounded down to the nearest multiple of the encoded block size. If {@code chunkSeparatorLength} is zero, then chunking is
      * disabled.
      * </p>
      *
      * @param unencodedBlockSize   The size of an unencoded block (for example Base64 = 3).
      * @param encodedBlockSize     The size of an encoded block (for example Base64 = 4).
      * @param lineLength           if &gt; 0, use chunking with a length {@code lineLength}.
      * @param chunkSeparatorLength The chunk separator length, if relevant.
      * @deprecated Use {@link BaseNCodec#BaseNCodec(AbstractBuilder)}.
      */
     @Deprecated
     protected BaseNCodec(final int unencodedBlockSize, final int encodedBlockSize, final int lineLength, final int chunkSeparatorLength) {
         this(unencodedBlockSize, encodedBlockSize, lineLength, chunkSeparatorLength, PAD_DEFAULT);
     }
 
     /**
      * Constructs a new instance.
      * <p>
      * Note {@code lineLength} is rounded down to the nearest multiple of the encoded block size. If {@code chunkSeparatorLength} is zero, then chunking is
      * disabled.
      * </p>
      *
      * @param unencodedBlockSize   The size of an unencoded block (for example Base64 = 3).
      * @param encodedBlockSize     The size of an encoded block (for example Base64 = 4).
      * @param lineLength           if &gt; 0, use chunking with a length {@code lineLength}.
      * @param chunkSeparatorLength The chunk separator length, if relevant.
      * @param pad                  byte used as padding byte.
      * @deprecated Use {@link BaseNCodec#BaseNCodec(AbstractBuilder)}.
      */
     @Deprecated
     protected BaseNCodec(final int unencodedBlockSize, final int encodedBlockSize, final int lineLength, final int chunkSeparatorLength, final byte pad) {
         this(unencodedBlockSize, encodedBlockSize, lineLength, chunkSeparatorLength, pad, DECODING_POLICY_DEFAULT);
     }
 
     /**
      * Constructs a new instance.
      * <p>
      * Note {@code lineLength} is rounded down to the nearest multiple of the encoded block size. If {@code chunkSeparatorLength} is zero, then chunking is
      * disabled.
      * </p>
      *
      * @param unencodedBlockSize   The size of an unencoded block (for example Base64 = 3).
      * @param encodedBlockSize     The size of an encoded block (for example Base64 = 4).
      * @param lineLength           if &gt; 0, use chunking with a length {@code lineLength}.
      * @param chunkSeparatorLength The chunk separator length, if relevant.
      * @param pad                  byte used as padding byte.
      * @param decodingPolicy       Decoding policy.
      * @since 1.15
      * @deprecated Use {@link BaseNCodec#BaseNCodec(AbstractBuilder)}.
      */
     @Deprecated
     protected BaseNCodec(final int unencodedBlockSize, final int encodedBlockSize, final int lineLength, final int chunkSeparatorLength, final byte pad,
             final CodecPolicy decodingPolicy) {
         this.unencodedBlockSize = unencodedBlockSize;
         this.encodedBlockSize = encodedBlockSize;
         final boolean useChunking = lineLength > 0 && chunkSeparatorLength > 0;
         this.lineLength = useChunking ? lineLength / encodedBlockSize * encodedBlockSize : 0;
         this.chunkSeparatorLength = chunkSeparatorLength;
         this.pad = pad;
         this.decodingPolicy = Objects.requireNonNull(decodingPolicy, "codecPolicy");
         this.encodeTable = null;
         this.decodeTable = null;
     }
 
     /**
      * Returns the amount of buffered data available for reading.
      *
      * @param context The context to be used.
      * @return The amount of buffered data available for reading.
      */
     int available(final Context context) { // package protected for access from I/O streams
         return hasData(context) ? context.pos - context.readPos : 0;
     }
 
     /**
      * Tests a given byte array to see if it contains any characters within the alphabet or PAD.
      *
      * Intended for use in checking line-ending arrays.
      *
      * @param arrayOctet byte array to test.
      * @return {@code true} if any byte is a valid character in the alphabet or PAD; {@code false} otherwise.
      */
     protected boolean containsAlphabetOrPad(final byte[] arrayOctet) {
         if (arrayOctet != null) {
             for (final byte element : arrayOctet) {
                 if (pad == element || isInAlphabet(element)) {
                     return true;
                 }
             }
         }
         return false;
     }
 
     /**
      * Decodes a byte[] containing characters in the Base-N alphabet.
      *
      * @param array A byte array containing Base-N character data.
      * @return A byte array containing binary data.
      */
     @Override
     public byte[] decode(final byte[] array) {
         if (BinaryCodec.isEmpty(array)) {
             return array;
         }
         final Context context = new Context();
         decode(array, 0, array.length, context);
         decode(array, 0, EOF, context); // Notify decoder of EOF.
         final byte[] result = new byte[context.pos];
         readResults(result, 0, result.length, context);
         return result;
     }
 
     // package protected for access from I/O streams
     abstract void decode(byte[] array, int i, int length, Context context);
 
     /**
      * Decodes an Object using the Base-N algorithm. This method is provided in order to satisfy the requirements of the Decoder interface, and will throw a
      * DecoderException if the supplied object is not of type byte[] or String.
      *
      * @param obj Object to decode.
      * @return An object (of type byte[]) containing the binary data which corresponds to the byte[] or String supplied.
      * @throws DecoderException if the parameter supplied is not of type byte[].
      */
     @Override
     public Object decode(final Object obj) throws DecoderException {
         if (obj instanceof byte[]) {
             return decode((byte[]) obj);
         }
         if (obj instanceof String) {
             return decode((String) obj);
         }
         throw new DecoderException("Parameter supplied to Base-N decode is not a byte[] or a String");
     }
 
     /**
      * Decodes a String containing characters in the Base-N alphabet.
      *
      * @param array A String containing Base-N character data.
      * @return A byte array containing binary data.
      */
     public byte[] decode(final String array) {
         return decode(StringUtils.getBytesUtf8(array));
     }
 
     /**
      * Encodes a byte[] containing binary data, into a byte[] containing characters in the alphabet.
      *
      * @param array A byte array containing binary data.
      * @return A byte array containing only the base N alphabetic character data.
      */
     @Override
     public byte[] encode(final byte[] array) {
         if (BinaryCodec.isEmpty(array)) {
             return array;
         }
         return encode(array, 0, array.length);
     }
 
     /**
      * Encodes a byte[] containing binary data, into a byte[] containing characters in the alphabet.
      *
      * @param array  A byte array containing binary data.
      * @param offset initial offset of the subarray.
      * @param length length of the subarray.
      * @return A byte array containing only the base N alphabetic character data.
      * @since 1.11
      */
     public byte[] encode(final byte[] array, final int offset, final int length) {
         if (BinaryCodec.isEmpty(array)) {
             return array;
         }
         final Context context = new Context();
         encode(array, offset, length, context);
         encode(array, offset, EOF, context); // Notify encoder of EOF.
         final byte[] buf = new byte[context.pos - context.readPos];
         readResults(buf, 0, buf.length, context);
         return buf;
     }
 
     // package protected for access from I/O streams
     abstract void encode(byte[] array, int i, int length, Context context);
 
     /**
      * Encodes an Object using the Base-N algorithm. This method is provided in order to satisfy the requirements of the Encoder interface, and will throw an
      * EncoderException if the supplied object is not of type byte[].
      *
      * @param obj Object to encode.
      * @return An object (of type byte[]) containing the Base-N encoded data which corresponds to the byte[] supplied.
      * @throws EncoderException if the parameter supplied is not of type byte[].
      */
     @Override
     public Object encode(final Object obj) throws EncoderException {
         if (!(obj instanceof byte[])) {
             throw new EncoderException("Parameter supplied to Base-N encode is not a byte[]");
         }
         return encode((byte[]) obj);
     }
 
     /**
      * Encodes a byte[] containing binary data, into a String containing characters in the appropriate alphabet. Uses UTF8 encoding.
      * <p>
      * This is a duplicate of {@link #encodeToString(byte[])}; it was merged during refactoring.
      * </p>
      *
      * @param array A byte array containing binary data.
      * @return String containing only character data in the appropriate alphabet.
      * @since 1.5
      */
     public String encodeAsString(final byte[] array) {
         return StringUtils.newStringUtf8(encode(array));
     }
 
     /**
      * Encodes a byte[] containing binary data, into a String containing characters in the Base-N alphabet. Uses UTF8 encoding.
      *
      * @param array A byte array containing binary data.
      * @return A String containing only Base-N character data.
      */
     public String encodeToString(final byte[] array) {
         return StringUtils.newStringUtf8(encode(array));
     }
 
     /**
      * Ensures that the buffer has room for {@code size} bytes
      *
      * @param size    minimum spare space required.
      * @param context The context to be used.
      * @return The buffer.
      */
     protected byte[] ensureBufferSize(final int size, final Context context) {
         if (context.buffer == null) {
             context.buffer = new byte[Math.max(size, getDefaultBufferSize())];
             context.pos = 0;
             context.readPos = 0;
             // Overflow-conscious:
             // x + y > z == x + y - z > 0
         } else if (context.pos + size - context.buffer.length > 0) {
             return resizeBuffer(context, context.pos + size);
         }
         return context.buffer;
     }
 
     /**
      * Gets the decoding behavior policy.
      *
      * <p>
      * The default is lenient. If the decoding policy is strict, then decoding will raise an {@link IllegalArgumentException} if trailing bits are not part of a
      * valid encoding. Decoding will compose trailing bits into 8-bit bytes and discard the remainder.
      * </p>
      *
      * @return true if using strict decoding.
      * @since 1.15
      */
     public CodecPolicy getCodecPolicy() {
         return decodingPolicy;
     }
 
     /**
      * Gets the default buffer size. Can be overridden.
      *
      * @return The default buffer size.
      */
     protected int getDefaultBufferSize() {
         return DEFAULT_BUFFER_SIZE;
     }
 
     /**
      * Gets the amount of space needed to encode the supplied array.
      *
      * @param array byte[] array which will later be encoded.
      * @return amount of space needed to encode the supplied array. Returns a long since a max-len array will require &gt; Integer.MAX_VALUE.
      */
     public long getEncodedLength(final byte[] array) {
         // Calculate non-chunked size - rounded up to allow for padding
         // cast to long is needed to avoid possibility of overflow
         long len = (array.length + unencodedBlockSize - 1) / unencodedBlockSize * (long) encodedBlockSize;
         if (lineLength > 0) { // We're using chunking
             // Round up to nearest multiple
             len += (len + lineLength - 1) / lineLength * chunkSeparatorLength;
         }
         return len;
     }
 
     /**
      * Tests whether this object has buffered data for reading.
      *
      * @param context The context to be used.
      * @return true if there is data still available for reading.
      */
     boolean hasData(final Context context) { // package protected for access from I/O streams
         return context.pos > context.readPos;
     }
 
     /**
      * Tests whether or not the {@code octet} is in the current alphabet. Does not allow whitespace or pad.
      *
      * @param value The value to test.
      * @return {@code true} if the value is defined in the current alphabet, {@code false} otherwise.
      */
     protected abstract boolean isInAlphabet(byte value);
 
     /**
      * Tests a given byte array to see if it contains only valid characters within the alphabet. The method optionally treats whitespace and pad as valid.
      *
      * @param arrayOctet byte array to test.
      * @param allowWhitespacePad if {@code true}, then whitespace and PAD are also allowed.
      * @return {@code true} if all bytes are valid characters in the alphabet or if the byte array is empty; {@code false}, otherwise.
      */
     public boolean isInAlphabet(final byte[] arrayOctet, final boolean allowWhitespacePad) {
         for (final byte octet : arrayOctet) {
             if (!isInAlphabet(octet) && (!allowWhitespacePad || octet != pad && !Character.isWhitespace(octet))) {
                 return false;
             }
         }
         return true;
     }
 
     /**
      * Tests a given String to see if it contains only valid characters within the alphabet. The method treats whitespace and PAD as valid.
      *
      * @param basen String to test.
      * @return {@code true} if all characters in the String are valid characters in the alphabet or if the String is empty; {@code false}, otherwise.
      * @see #isInAlphabet(byte[], boolean)
      */
     public boolean isInAlphabet(final String basen) {
         return isInAlphabet(StringUtils.getBytesUtf8(basen), true);
     }
 
     /**
      * Tests true if decoding behavior is strict. Decoding will raise an {@link IllegalArgumentException} if trailing bits are not part of a valid encoding.
      *
      * <p>
      * The default is false for lenient decoding. Decoding will compose trailing bits into 8-bit bytes and discard the remainder.
      * </p>
      *
      * @return true if using strict decoding.
      * @since 1.15
      */
     public boolean isStrictDecoding() {
         return decodingPolicy == CodecPolicy.STRICT;
     }
 
     /**
      * Reads buffered data into the provided byte[] array, starting at position bPos, up to a maximum of bAvail bytes. Returns how many bytes were actually
      * extracted.
      * <p>
      * Package private for access from I/O streams.
      * </p>
      *
      * @param b         byte[] array to extract the buffered data into.
      * @param position  position in byte[] array to start extraction at.
      * @param available amount of bytes we're allowed to extract. We may extract fewer (if fewer are available).
      * @param context   The context to be used.
      * @return The number of bytes successfully extracted into the provided byte[] array.
      */
     int readResults(final byte[] b, final int position, final int available, final Context context) {
         if (hasData(context)) {
             final int len = Math.min(available(context), available);
             System.arraycopy(context.buffer, context.readPos, b, position, len);
             context.readPos += len;
             if (!hasData(context)) {
                 // All data read.
                 // Reset position markers but do not set buffer to null to allow its reuse.
                 // hasData(context) will still return false, and this method will return 0 until
                 // more data is available, or -1 if EOF.
                 context.pos = context.readPos = 0;
             }
             return len;
         }
         return context.eof ? EOF : 0;
     }
 }